I would use warm water with detergent....then rinse with more warm water and dry with a micro-fiber cloth. You get those at your friendly local optometrist...they're used for (primarily) plastic lenses on your glasses.

You could also purchase an "over the counter" cleaning kit for CDs.

I've even had some success at removing scratches from a CD by buffing them out with a very soft "grinding compound"....... TOOTHPASTE!

Just make sure that you wipe in a circular pattern and don't "polish" any more than necessary to get the CD player to track properly! (and it might be a dead loss in any case....but what have ya got to lose?)

First rinse off any loose/gross material with a light pressure sink sprayer, then soak as Tootsall mentioned, in a warm water & Dawn dishwashing soap. After soaking for 30-60 minutes, spray again any material from the surface, then, under water, use a micro fiber cloth to wipe from the center hole outwards (radially) to remove any last material, then rinse thoroughly and dry by wiping radially with the micro cloth.